This invention relates to telescoping antennas, and more particularly to a telescoping antenna having an indicator which indicates the degree of telescoping necessary to achieve a predetermined antenna length.
Telescoping antennas have been in wide use for many years for signal reception and transmission to radios, televisions and the like. One of the most widespread uses for telescoping antennas has been on vehicles as vehicle radios became a common vehicle accessory. In years past vehicle radios were generally AM radios and thus the longer the telescoping capability of the antenna the better the radio reception, especially of distant signal broadcasts. However, in recent years the AM-FM radio unit has gained increasing popularity. Unlike the case with AM reception where any increase in antenna length generally improves the strength of signal pick-up because of the short AM wavelengths, the relatively long FM wavelengths on the order of 124 inches require incremental increases in length to improve reception without distortion, such as in quarter, half, or full wavelength increments. In the case of the FM band frequencies employed in home and vehicle FM radios, the mean quarter wavelength is approximately 31 inches. Thus, optimum antenna lengths for this FM reception range would be approximately 31, 62, 93, 124 inches, etc.
Because of many problems inherent in unduly long antennas on moving vehicles, e.g. strength, overhead obstructions, etc., aside from special applications, the vehicle antenna industry has generally standardized on antennas with extended lengths less than 60 inches. Thus, the goal in antennas for optimum FM reception has been an extended length of approximately 31 inches. In fact, one of the more widely used type of vehicle antenna today has a non-telescoping antenna mast with a fixed length of 31 inches. This type of antenna optimizes FM reception while yielding acceptable AM performance where the AM broadcast signals are relatively strong.
Nevertheless, there still exists a strong market for telescoping antennas which achieve antenna lengths greater than 31 inches to enhance reception of weaker AM broadcast signals. Furthermore, it is desirable that telescoping antennas be capable of telescoping to less than 31 inches to minimize bending and breaking problems in car washes, etc., to which telescoping antennas are susceptable. Thus, the ideal telescoping antenna today would be one which has an extended length greater than 31 inches and a collapsed length less than 31 inches, but one which can also be easily and conveniently set at a length of 31 inches to optimize the FM reception.